Growth of the non-pubescent child is ideally studied by using children with congenital heart disease as a model because significant growth disturbance is frequent, corrective surgery is effective and postoperative growth acceleration is common. This study measures the growth of these children by measuring changes in body fluids, body electrolytes, and body composition as these changes relate to such anthropometric measurements as height, weight, assessment of leanness-fatness and skeletal age. These studies will be done before cardiac surgery to assess the nature of the growth failure frequently seen. Such studies will be repeated in the postoperative period to assess the contribution of the various body compartments to growth as well as to delineate the time sequence at which increases in various body compartments take place. Although normal growth data is available during the non-pubescent age period, no longitudinal study specifically dealing with the non-pubescent child who undergoes rapid growth acceleration has been published.